[jhb] Re: Which Speed?
- From: "bones" <bones@xxxxxxx>
- To: <jhb@xxxxxxxxxxxxx>
- Date: Mon, 2 Jul 2007 16:00:21 +0100
Yep - you are pushing FS beyond its limitations here.
Forget real aircraft values for this exercise. The issue is with the
aircraft performance file and if the designer hasn't got this locked down to
the performance of the real aircraft then you aren't testing an A350 or DC10
but a mythical design - for which a full flight test program needs carrying
out to find it's boundaries.
Any aircraft will lift off at stall speed - because this is the minimum
speed for flying and you are accelerating past this on take off. FS models
the low speed performance awfully so accept that designers can't get this
right all the time and that variation exists. Another thing is that you say
there are discrepancies between some models and the real aircraft but where
did you get real aircraft values from? The stall speed varies with a huge
number of factors - weight, ISA, flap setting are the obvious ones - but it
varies between aircraft fleets too as the aircraft specification may change.
A Boeing 737-8AS or Ryanair will have different figures for a Boeing 737-8K7
of Austrian Airlines. That is why performance manuals are written for
specific aircraft - even the two PA31 aircraft I used to fly had different
figures.
The best you can do in FS is to hand fly each aircraft and determine your
own values - forget any book figures quoted from real manuals.
bones
-----Original Message-----
From: jhb-bounce@xxxxxxxxxxxxx [mailto:jhb-bounce@xxxxxxxxxxxxx] On Behalf
Of Gerry Winskill
Sent: 02 July 2007 11:27
To: jhb@xxxxxxxxxxxxx
Subject: [jhb] Re: Which Speed?
What triggered off this Quest was the thought that I should rationalise
the aircraft kept in my FSX Airplanes folder, so that it would hold only
those I use, plus those required as AI. The others were moved to my FSX
Hangar.
So, I finished up with a restricted fleet of 4 GA aircraft and 8 others.
The "others" were
CITATION II
B1900D, PDMG
DASH8 Q400, Dreamwings
CRJ900, POSKY
A320 (BA), IFDG
ERJ145, Dreamwings
A350, CamSim
A340-313, Aerodesigns
Most had a Vspeed gauge with speeds related to published weight and V
number data but I decided to run all of them through the checks I'd
carried out on the A350, so that Vspeeds reflect the simulated aircraft.
I also threw into the tests the Default A321.
Main criteria for selecting the fleet was what seemed to be acceptably
realistic performance, although the Dash8 doesn't behave as well in FSX
as it did in FS9.
The results showed slight discrepancies between the takeoff speeds and
those of the real aircraft; with two exceptions. I do the tests at MTOW
and a minmum weight, so that the gauge has a range to use. In the case
of two of them I didn't bother with the lower weight. At MTOW and just
the 12 degrees of flap deployed the A340 lifted off at 108 kias! Since I
normally fly it with elevator trim set at 10, instead of the 80 I use
for these tests, I would rotate, at this weight, at the more realistic
156 kias and not spot that it would have been able to lift off much
earlier, particularly since its acceleration is what would be expected.
I can't think of a simple way of altering the lift off speed, without
suffering knockon effects where I don't want them. So it looks a though
the A340 is heading for the Hangar.
The Default A321, at max weight and just the first degree of flap set,
takes to the sky at a slightly unbelievable 95 kias! It's used by AI or
it would be dustbin bound.
The expression "can of worms" starts to surface.
Gerry Winskill
I
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